My invention relates generally to infinitely variable belt drives of the kind disclosed, for example, in my prior U.S. Pat. No. 3,115,049. Another transmission structure capable of embodying the improvements of my present invention is shown in U.S. Pat. No. 3,600,960.
Infinitely variable belt drives usually include adjustable sheaves located on parallel axes. The pitch of the sheaves can be changed to effect variations in torque ratio. One sheave serves as a torque input member and the other sheave serves as a torque output member.
These infinitely variable belt drives normally require axial clamping forces to prevent slippage of the belts with respect to the sheaves. The sheaves normally have conical surfaces situated in juxtaposed relationship and the axial distance between the sheaves can be changed thereby controlling the effective pitch diameter of the sheaves. To effect the clamping forces necessary to prevent belt slippage, hydraulic piston and cylinder assemblies are used. These act in cooperation with hydraulic piston and cylinder assemblies that are used to control the ratio.
The pressure for the control system necessary to achieve the torque ratio control and the belt clamping control is supplied by an oil pump that must be driven by the engine with which the transmission is used. Because of the high clamping forces necessary in the prior art constructions, the oil pump must achieve a high pressure and this results in high parasitic power loss.